The present invention relates to a sealing apparatus for picture tubes which seals a glass bulb including a phosphor screen formed therein and a stem structure mounted with an electron gun structure.
Generally speaking, in the process of manufacturing a color picture tube, the phosphor screen, a graphite electrode and a shadow mask are provided inside the glass bulb. Subsequently, the stem structure mounted with the electron gun structure is sealed at the opening end of a glass bulb neck portion. This kind of sealing method is disclosed in the specification of Japanese Patent Publication No. 31595/1978. The sealing operation of the thus constructed picture tube requires a sealing apparatus for the picture tube which will be explained as follows.
FIG. 2 is a construction diagram in plan of the principal portion of one example of a commonly used sealing apparatus for the picture tubes. It can be observed from the figure that a plurality of bulb holders 11 for holding, with the tube-axis being centered, the above-described glass bulb are regularly disposed with equal spacings on the outer peripheral portion of a disclike index table 10. These bulb holders 11 are rotated together with the index table 10 at a predetermined velocity and pitch in the direction indicated by an arrow A by means of an automatic driving device (not illustrated). More particularly, the bulb holders 11 are moved to specified positions at given intervals in a highly accurate manner by an index driving device (not illustrated). The respective bulb holders 11 disposed on the index table 10 are usually brought into a state of installing and removing the glass bulb in positions #1 and #2 of FIG. 2. The neck portion and the sealing portion are preheated in positions #3 to #8; the bulb neck portion is welded in a position #9; fusion-cutting is effected in a position #10; slow cooling is carried out in positions #11 to #15; and a piece of neck tube (ordinarily referred to as cullet glass) separated from the bulb neck portion by the aforementioned fusion-cutting is removed in a position #16.
FIG. 3 is a side view showing the principal portion of the well known bulb holder 11 described in FIG. 2. In the Figure, the bulb holder 11 is arranged such that a glass bulb 1 including the phosphor screen, the graphite electrode and the shadow mask which are formed therein is fixed in a retainable manner to a present reference spot by a bulb holder unit 17 consisting of a bulb stopper 12, a panel chuck 13, a bulb support 14, a holder frame 15 and a bulb holder 16, etc., and this bulb holder unit 17 is likewise supportingly fixed onto the index table 10 by a support 18. With the tube-axis being centered, beneath the bulb holder unit 17 is disposed a mount pin 19 equipped with a stem structure 3 mounted with an electron gun structure 2. This mount pin 19 causes the stem structure 3 to be driven both in the rotational direction and in the vertical direction.
In such a configuration, the stem structure 3 on which the electron gun structure 2 is loaded is installed on the mount pin 19 in a roughly adjusted state and is then raised to be inserted in a bulb neck portion 1a. The electron gun structure 2 is positioned at a predetermined height by slightly adjusting the mount pin 19 in the rotational and vertical directions. In addition, an outer peripheral surface of the neck portion 1a, corresponding to the same height as a stem glass 3a of the stem structure 3 is, as illustrated in FIG. 4, heated with flames 21 generated by gas burners 20. As depicted by solid lines, the neck portion 1a and the stem glass 3a are welded to each other, thereby sealing these two members. At the same instant, cullet glass 1a', which is suspended down from the thus welded portion, of the neck portion 1a is melted and separated. At this time, the thus melted and separated cullet glass 1a' remains on a mount pin base 19a of the mount pin 19. The reference symbol 3b stands for an exhaust tube.
In the above-described sealing apparatus, a heating system 22 (hereinafter referred to as a working head) designed for glass processing which is equipped with the gas burners 20 shown in FIG. 5 or with a hot air heater unit that will be mentioned later is fixedly so disposed outside the index table 10 as to make this working head 22 apart from the mount pin 19 in order not to come in contact with the index table 10. In this type of apparatus, where, for instance, working heads illustrated in FIGS. 6a, 6b and 6c are employed, a hot air 34 or burner flames 44, 54 do not impinge precisely upon the neck portion 1a in some cases because of disturbances of airflow in the circumference thereof. When instantaneous heating is needed, it is feasible to effect heat processing with high efficiency for a short period of time by heating simultaneously the overall periphery of the neck portion. The above-mentioned apparatus is, however, defective in that it is difficult to reduce the heating time and still provide a high yield effect on account of the heating operation being performed from one side alone of the neck portion. In the conventional apparatus, as described above, the heating spot of the bulb neck portion 1a is apt to undergo influences such as external disturbances and hence highly accurate heat processing becomes impossible. Concomitantly, it is also difficult to increase the heating rate.
Especially, in the glass bulb having the so-called culletless neck portion so formed as to shorten a neck length without providing a brimlike opening end portion at the tip of the glass bulb neck portion 1a, or in its sealing apparatus, when adopting the above-described conventional burner processing system, it is difficult to melt down the tip alone of the neck portion in a short time with a high degree of accuracy and at the same time preventing the flames from heating the metallic lead wires which support the electron gun.
FIGS. 6(a) to 6(c) are schematic plan views each showing a conventional working head 24. The working heads 24 shown in FIGS. 6(a), 6(b) are prepared for preheating and annealing processes. On the other hand, the working head 24 shown in FIG. 6(c) is used for a glass softening process. In FIG. 6(a), such is the situation that a high pressure gas introduced in the direction indicated by an arrow 32 passes through a hot air heater unit composed of a heater 33 and a cylinder 31, in which unit the gas is changed into a hot air jet 34 for heating the neck portion 1a. In FIG. 6(b), a mixture of natural gas and air fed in the direction pointed by an arrow 42 passes through a gas air burner 41 where the mixture is converted into a soft flame 44 which heats the neck portion 1a. In FIG. 6(c), a mixture of the natural gas and oxygen which is introduced in the directions indicated by the arrows 42 does through oxygen burners 51 where the mixture is converted into a hard flames 54 so as to heat the neck portion 1a. In each of the aforecited conventional working heads, it is unfeasible to uniformly heat the overall periphery of the glass bulb neck portion 1a, simultaneously thereby resulting in a difficult to perform instantaneous heating operation. Furthermore, it is impossible to effect the heat processing with high accuracy because of the external disturbances being present, since the burners or the hot air heater unit are/is disposed considerably apart from the neck portion 1a.